Seadall is actually one of the most important characters to keep in your party in Fire Emblem: Engage. Despite him showing up late and looking kind of weird.

He’s not super important to the story, but the reason you want to keep them in there…

Is because he is the only dancer class of the game. Which allows you to give one character an extra turn. And if you pair him with Byleth, you can actually use the goddess dance to do it to four other characters every now and then. Which can definitely make or break certain missions.

I used his dance so much that he leveled up naturally from it and by the end of the game he was actually fairly decent warrior despite not being in an offensive class, lol.